It is frequently desirable and often mandatory to provide emergency lighting units as sources of limited but useful illumination upon the loss of AC power for any reason. Such units are particularly imperative in areas such as theaters, hallways, and windowless rooms which are totally dependent on artificial lighting for useful illumination. Emergency lighting units typically contain a battery as a source of electrical energy, a low voltage lamp for providing the emergency illumination, sensing means for detecting the loss of AC power, and a switch for instantaneously connecting the battery to the low voltage lamp to provide illumination upon loss of power. In most instances, a rechargeable wet battery is used as the emergency power source, with means to maintain a full charge whenever normal AC power is available. Two exemplary emergency lighting units are shown in U.S. Pat. Nos. 1,922,079 and 3,294,977.
One of the principal disadvantages of most emergency lighting units known to the prior art is that these units are distinct and separate accessories which are located within the area to be protected without any other function. The wall-hung boxes with projecting sealed-beam bulbs seen in theaters and restaurants are perhaps the most common illustrations of units which cannot be successfully integrated into the functional and decorative arrangements of the premises to be protected but, rather, have the appearance of being afterthoughts. Furthermore, the fact that such units are not functionally integrated with the remainder of the room means that separate wiring facilities must frequently be provided for supplying power, and their positions on walls or partitions often require the use of unsightly goosenecks or similar contrivances to direct the emergency illumination to the required area. For these reasons and others, emergency light sources have not been used in many areas such as rooms in homes and hospitals which should be protected by an emergency lighting system to avoid dangerous conditions arising from a sudden loss of illumination upon failure of the AC power system.
The concept of emergency lighting in the configuration of a table lamp is not in itself new; see, for example, the present applicant's U.S. Design Patent D-212,443. This patent shows a table lamp having customary light bulbs powered, in normal operation by the AC line. Upon power failure, a much smaller bulb is lighted from a battery to provide an acceptable level of emergency illumination.
While such lighting units have been proposed, they have not been either widely available or in common use. Emergency lighting must be extremely reliable to gain acceptance; on the other hand, for a table unit it is absolutely essential that reliability be achieved with minimum cost and with a mechanical structure that permits ease of service with an overall aesthetic appearance.